1. Field of the Invention
This invention relates to an improved method of electroslag welding involving the use of a fiberized flux in blanket form.
2. Description of the Prior Art
Electroslag welding is well known. In general, when weld-joining plates or bars, the work piece is horizontally arranged with the vertical edge surfaces of the plates substantially uniformly spaced and fixed in spaced relationship by a metallic strip or bar spanning the bottom of the cavity formed between the vertical edge surfaces of the plates to be weldably joined. The bottom strip is not only utilized to permit starting the welding procedure, but also serves to restrain or restrict heat distortion of the joint during the welding procedure. Sometimes the bottom strip may be supplemented by reinforcing bars forming a "strong back" to further resist heat distortion. The ends of the cavity are closed by water-cooled copper dams or shoes to avoid loss of molten weld metal and slag during the welding procedure.
In electroslag welding the welding head usually includes a consumable guide member of generally rectangular horizontal cross section and is provided with one or more slots or apertures which serve to permit downward movement of electrode or filler wires therethrough, through which electric power is supplied for the welding procedure. In general, the guide member substantially extends the full length of the cavity to be filled with weld metal and is dimensioned to provided a gap between the exterior longitudinal walls thereof and the adjacent vertical edges of the plates to be weld joined. Under such dimensional circumstances, the guide is substantially stationary insofar as transverse movements are concerned. Under some circumstances, however, the guide member is of the non-consumable type where it becomes necessary to change the vertical relationship of the guide member relative to the weld cavity. The more common procedure is to utilize consumable guide members where the member is generally fixed in a vertical direction insofar as the weld cavity is concerned.
In the procedure heretofore in use, it has been customary to provide granular flux or slagging material through the gap between the edge of the guide member and the vertical member of the plate to be welded. To start the welding procedure, it has also been customary to insert a starter material, such as steel wool, directly under the electrode wires and extending through the granular flux so that the initial flow of electric current can occur through the steel wool. Once the welding procedure has been started, the flux or slag material which is substantially non-conductive in its cold granular form is melted by passage of the current through the steel wool. With the arc initially established, the granular slag melts and becomes relatively electrically conductive and forms a molten pool which covers the surfaces of the work piece being welded. As the procedure continues, the molten flux provides a protective layer on the top of the molten weld metal to avoid oxidation and harmful slag inclusions in the weld so formed.
In the procedure heretofore in use, an enlarged gap between the guide and the work piece surfaces prevented short circuiting, by physical contact or arcing, of the welding process. It is obvious that an enlarged cavity would not only prevent short circuiting, but also would provide easy access to the slag pool to which additional flux may be supplied as needed. The increased volume of the cavity, however, increases the amount of filler material to be deposited, increases the amount of flux material to produce the necessary slag pool and also causes excessive heating produced by the additional filler material resulting in degradation of the mechanical properties of the weld zone in many of the low alloy and high strength steels. Therefore, it is desirable to separate the surfaces of the work pieces by a narrow gap having an insulating material situated between the guide and the work pieces. Filling a narrow gap with typical granular flux is generally inadequate with respect to the necessary electrical insulation, since the granular flux has a tendency to surge into the slag pool leaving an inadequate narrow air space for electrical insulation purposes.
Electrically insulating material, such as ceramic refractory fibers and glass wool disposed within the gap with the granular flux have been suggested as a means of correcting the loss of granular flux insulation. In general, however, these materials have been found to adversely influence the weld properties.